Advancing age is associated with insulin resistance, glucose intolerance, and Type 2 diabetes. Regular higher-intensity aerobic exercise reduces insulin resistance and lowers the risk of Type 2 diabetes. Nonetheless, recent cross-sectional data, based on ACSM/CDC physical activity recommendations for moderate-intensity activity on most if not all days of the week (i.e., 1000 kcal/wk), demonstrate that insulin levels are lower with regular moderate-intensity activity in middle-aged adults, suggesting a reduction in insulin resistance. Despite these cross-sectional data, few well-controlled prospective studies have determined if these recommendations are appropriate to reduce insulin resistance in the elderly. Because higher-intensity aerobic exercise is not practical for a large percentage of the elderly, data are needed to determine the efficacy of moderate-intensity exercise on reducing insulin resistance. Therefore, the primary aim of this study will be to examine the influence of 1000 kcal/wk of moderate versus higher-intensity aerobic exercise on insulin-simulated glucose disposal. A secondary aim will examine if moderate and higher-intensity aerobic exercise differentially influence non-exercising activity. Recent data in the elderly suggest that regular higher-intensity activities may reduce non-exercising activity during rest of the day. We will recruit 57, 65-90 y old women and men, who will be randomized into one of the following three groups: 1) Moderate-intensity activity (1000 kcal/wk at 50 percent VO2peak; 2) Higher-intensity activity (1000 kcal/wk at 75 percent VO2peak); 3) Control. Subjects will complete 12 wk of aerobic cycling with pre and post-testing for insulin-stimulated glucose disposal via the hyperinsulinemic/euglycemic clamp, glucose tolerance by an OGTT, and body composition using dual energy x-ray absorptiometry. Physical activity levels will be assessed by structured questionnaire every 3 weeks. Our primary hypothesize is that 1000 kcal/wk of moderate or higher-intensity activity will be equally effective decreasing insulin resistance in the elderly. Our secondary hypothesis is that higher-intensity activity will decrease non-exercising physical activity in the elderly. This New Investigator application will provide data to base future aerobic exercise recommendations in elderly adults.